I have Java installed in /home/ubuntu under the directory:
/home/ubuntu/jre1.6.0_06

In the directory for Firefox profile, i.e. /home/ubuntu/.mozilla there
should be a subdirectory named: plugins

In the directory, /home/ubuntu/.mozilla/plugins there should be the
following symbolic link that needs to be made to complete the
installation of java with this setup, as follows:
lrwxrwxrwx 1 ubuntu ubuntu 61 2008-09-15 07:07
libjavaplugin_oji.so -
/home/ubuntu/jre1.6.0_06/plugin/i386/ns7/libjavaplugin_oji.so

In order to accomplish the symbolic link (if you do not have it),
issue the following commands from /home/ubuntu as ubuntu regular user:
$ cd .mozilla/plugins
$ ln -s
where is:
home/ubuntu/jre1.6.0_06/plugin/i386/ns7/libjavaplugin_oji.so
and is: libjavaplugin_oji.so

If you have installed java elsewhere as you indicate in /usr/lib/jvm,
only the absolute full target pathname of the same file will be
different to install the symbolic link above in your Firefox profile.
You will need to find the libjavaplugin_oji.so file under /usr/lib/jvm
and use its full absolute file pathname to create the symbolic link as
above.

You should be able to verify your installation of java plugin in a
Firefox tab or window by typing into the address location bar the
following: about:plugins
and it should tell you that about all of your install plugins. In
fact, I recommend that you try this first to see what it says about
the java plugin if anything.